Process of producing pure iron



Patented Feb. 17, 1931 WALTER CLARK, LOS ANGELES, CALIFORNIA PROCESS O1? PRODUCING PURE IRON No Drawing. Application filed April 22,

My invention relates to a process of producing carbon free iron or iron showing a very low carbon content.

The development of desirable characteris- 5 tics in so-called alloy steels or alloys of iron with chromium and'a number of othermetals is to a great extent dependent on the purity of-the iron or the absence of carbon in the iron forming the basis of the alloy. It is 1 an object of this invention to provide a-simple, efiicient and economicprocess whereby iron may be treated to reduce the carbon content thereof to an exceedingly low point so that for practical purposes it may be considered as carbon free iron.

My invention is based on m discovery that when molten iron is'treate with air in a manner similar to the Bessemer process, carrying this to a' point where a certain proportion of the iron is converted into oxide; then the air in the Bessemer converter is displaced I by an inert gas and finally a blast of hydrogen passed through the molten mass and the iron oxide, the high temperaturenecessary to the reduction of the carbon content of the unoxidized iron is eifected when the oxide itself is reduced to metallic iron..

My invention consists in the steps of the process hereinafter described and claimed.

My process is not dependent on any particular apparatus but I prefer to use the well known Bessemer converter and in the molten ironin such converter I introduce air heated as high as possible, which temperature should not be less than 700 F. Since oxygen is the active agent desired, oxygen can'be substituted therefor or mixed with some other inert. gas but air will answer the purpose and the, use of it is much more convementl and less expensive.

The heated air is blown underpre'ssure' through the mass of molten iron until approximately three-quarters of the iron is converted into oxide. The formationbf the oxide increases the bulk of the mass considerably, therefore allowance .for this-increase should be made in determining the mass of molten-iron in the converter. At this state I introduce a blast of inert gas, preferably.

under the same pressure and temperature'as 1929. Serial No. 357,357.

the air supplied in the preceding step, to displace and remove any air from the converter and the mass of iron and oxide. The inert gases preferred are helium, argon or nitrogen the helium or argon being preferred placed by carbon free hydrogen under pres-.

sure and with the same degree of temperature preferably as the air previously used 7 and the. combined mass of the molten iron and iron oxide is subjected to the hydrogen blast until all the oxides of iron are reduced to metallic form, after which the hydrogen blast is continued until the carbon is reduced to its lowest point or eliminated. The end of the reaction .is determined by experience and by the color of the hydrogenflame issuing from the mouth of the converter.

The above treatment of the molten iron to so reduce the carbon content will also remove other impurities of the iron, if such" be present, such as silicon, sul hur and phosphorgus. The carbon content c the iron thus treated has been as low as 002.

As a modification of the above process, in case a particular composition-containing carbon is required, a predetermined quantity of 'high'ca'rbon steel or high. carbon alloy may I I be added, in which event the hydrogen blow so should be interrupted immediately after the introduction of the carbon contammgsteel or alloy to avoid loss of carbon. The finished 'metal; whether in the carbon free state or with-the predetermined carbon content may cs now be cast directly from the converter mto ingot moulds or poured into a ladle and repoured from. the ladle. Itis desirable to carry a film or coating of slag over the surface of the molten metalup to the instant of pouring, to avoid the collection of carbon or other extraneous matter.

It has been found that iron produced by this method of operation is clean and when cast in ingot moulds, cools with but little sinking or piping and that alloys, especially chromium iron alloys produced under this process are of exceptionally good quality and free of hard spots.

Under the process above disclosed it will be possible to produce chromium'iron alloys and other alloys for which pure iron is an essential base, at a cost below that at which alloys of equal grade are now produced. For instance, a so-called stainless steel can be produced where the carbon free iron is used as a base by adding as low a percentage as from 9 to 14: percent of chromium, while with the ordinary iron with its carbon content a considerably higher percentage of chromlum 1s required.

Various changes may be made by those skilled in the art, in the steps of my process without departing from the spirit of my invention as claimed.

I claim:

1. A process of treating iron to produce substantially carbon free iron comprising melting the iron in a closed chamber, blowing heated air through the body of the iron until about three-quarters of the iron is converted into oxide, displacing the residual air with nitrogen and blowing heated hydrogen through the mass until the oxide is reduced to metal and until the carbon content of the iron is reduced to the desired point.

2. A rocess of treating iron to produce substantially carbon free iron comprising blowing heated air through a molten body of iron in a closed chamber until a major part of the iron is converted into oxide, displacing the residual air with a chemically inert gas, blowing heated hydrogen through the mass until the oxide is reduced to metal'and until the carbon content of the iron is reduced to the desired point. p

In testimony whereof I have signed my name to this specification.

WALTER GORDON CLARK. 

